Primarily, this experimental effort will be to characterize the agents of viral hepatitis through studies of two nonhuman primate models: chimpanzees and mystax marmosets. Experimental protocols developed by the Project Officers will be carried out by personnel qualified and experienced in the care and handling of nonhuman primates. These effortsmay focus on pathogenicity, immunology, and vaccine development for various forms of viral hepatitis. As a basic objective, the primate colony will serve as a source of blood and tissue specimens at various stages of infections. As an adjunct to the primate studies, a colony of woodchucks will be maintained for investigations of woodchuck hepatitis and a hepatocellular carcinoma, as well as vaccine and cross-vaccination studies.